Bug 498223

Summary: X11 session mouse curosor extremly laggy and delayed
Product: [Plasma] kwin Reporter: William <Wi11iam_1>
Component: platform-x11-standaloneAssignee: KWin default assignee <kwin-bugs-null>
Status: RESOLVED UPSTREAM    
Severity: normal CC: xaver.hugl
Priority: NOR    
Version First Reported In: 6.2.5   
Target Milestone: ---   
Platform: openSUSE   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description William 2025-01-03 19:36:17 UTC 
Only in the X11 session the mouse cursor is extremely laggy and delayed (like dragging it on a rope). This however stops as soon as some effect is running that updates the forces the screen to be updated.
e.g. when running glxgears at monitor refresh rate in background the cursor is normal. as soon as glx gear is stopped and only some static apps are running that do not update the screen every vblank the cursor becomes very slow.
using the showFPS effect also forces the screen update and therefor fixes the cursor but as soon as its deactivated the cursor is slow again.

Note: cursor is also slow when compositing is disabled (kwin_x11 suspend). only X11 is affected, in wayland the cursor behaves normaly.

SOFTWARE/OS VERSIONS
Linux Kernel:  6.12.6
KDE Plasma Version:  6.2.4
KDE Frameworks Version: 6.9.0
Qt Version: 6.8.1

ADDITIONAL INFORMATION
single dedicated AMD gpu, displayport connection to single monitor that does not support "freesync" or other VRR.
Comment 1 Zamundaaa 2025-01-03 19:57:28 UTC 
KWin isn't involved in cursor rendering on Xorg, this is a kernel or Xorg DDX bug
Comment 2 William 2025-01-03 20:17:54 UTC 
then why does it only happen in plasma and stops as soon as kwin_x11 renders some other stuff?
Comment 3 Zamundaaa 2025-01-03 22:00:42 UTC 
I don't know. As I already wrote, it's not something kwin_x11 is responsible for or interacts with. Bugs can be really weird sometimes.